Management of Organic Waste Part 3 docx

Anaerobic Treatment and Biogas Production from Organic Waste 21 balances out, pre-treatment may have benefits such as more stable digested substrate, smaller digesters, pathogen removal etc. There are substrates that require extensive pre- treatment; especially this is the case for ligno-cellulosic material (like spent brewery grains, Sežun et al. 2011) that require energy intensive pre-treatment to be successfully digested. In such cases the energy need for pre-treatment must be accounted in the energy production. In many cases it cannot outweigh the economy of the process; it may well happen that the parasitic energy demand is too high. Fig. 11. Schematic of a combined heat and power units (CHP) unit In recent years great interest was taken to biogas injection into natural gas grid. Mainly due to the fact, that global energy efficiency in such cases is usually far greater that at CHP plants. Namely in warmer periods of the year, heat produced in the CHP is largely wasted and therefore unused. Injecting the biogas into natural gas grid assures more than 90% energy efficiency, due to the nature of the use (heat production), even in warmer periods. Consequently the whole biogas production process can be more economic, in some cases even without considerable subsidies as well as more renewable energy is put to the energy supply. Also in most cases, the investment costs of biogas plants may be less, since there is no CHP plant. In order to be able to inject the biogas into natural gas as biomethane (Ryckebosch et al., 2011) grid certain purity standards must be fulfilled, which in EU are determined by national ordinances (a good example is the German ordinance for Biogas injection to natural gas grids from 2008), where responsibilities of grid operators and biogas producers are determined (Fig. 13) as well as quality standards are prescribed (DVGW, 2010). When injecting biomethane into the natural gas grid some biogas must be used for the Management of Organic Waste 22 reactors self-heating. It is advisable to use regeneration (Fig. 12), even in mesophilic temperature ranges, to minimize this expenditure, which on annual basis can contribute to 10-20 % of all biogas production (Pöschl et al., 2010). Fig. 12. Scheme of the heat regeneration from output to input flows. Fig. 13. Injection of biogas into natural gas grid (Behrendt and Sieverding 2010) 3.5 Anaerobic digestion residue management Environmental impact assessment of an anaerobic digestion plant (a biogas station) should take into consideration both the plant emissions and the digestate management. The first aspect mainly relates to flue gas and odour emissions. The exhaust gases from gas motors must fulfil emission limit values, which is not a problem when appropriate gas pretreatment Anaerobic Treatment and Biogas Production from Organic Waste 23 (sulphide and ammonia removal) has been applied. Unpleasant odours mainly originate from storage, disintegration and internal transport of organic waste. These should be carried over in a closed system, equipped with an air collection system fitted with a biofilter or connected with the gas motor air supply. 3.5.1 The anaerobic digestion residue management A quality management system (QMS) specific to a defined digestion process and its resulting whole digestate or any separated liquor and separated fibre, should be established and maintained. Anaerobically digested slurry or sludge contains 2-12 % of solids; wet waste from solid state digestion contains 20-25 % solids. The digestate contains not degraded organic waste, microorganism cells and structures formed during digestion, as well as some inorganic matter. This is potentially an alternative source of humic material, nutrients and minerals to the agricultural soil (PAS, 2010). It may be used directly or separated into liquid and solid part. The liquid digestate is often recycled to the digestion process; some pretreatment may be required to reduce nitrogen or salt content Freshly digested organic waste is not stable under environmental conditions: it has an unpleasant odour, contains various noxious or corrosive gases such as NH 3 and H 2 S, and still retains some biodegradability. In certain periods of a year it may be used in agriculture directly, in most cases however it must be stabilized before being applied to the fields. Aerobic treatment (composting) is an obvious and straightforward solution to this problem. The composting procedure has several positive effects: stabilization of organic matter, elimination of unpleasant odours and reduction of pathogenic microorganisms to an acceptable level. Composting, applied prior to land application of the digested waste, contributes also to a beneficial effect of compost nitrogen availability in soil. (Zbytniewski and Buszewski, 2005; Tarrasón et al., 2008) The simplest way is composting of the dehydrated fresh digestate in a static or temporarily turned-over pile. A structural material is necessary to provide sufficient porosity and adequate air permeability of the material in the pile. Various wood or plant processing residues may be used as a structural material like woodchips, sawdust, tree bark, straw and corn stalks provided that the sludge : bulk agent volume ratio is between 1:1 and 1:4 (Banegas et al., 2007). The majority of organic material is contributed by the bulking agent, but significant biodegradation of the digestate organic material also occurs, by means of natural aerobic microorganisms. The final compost quality depends on the content of pollutants such as heavy metals, pathogenic bacteria, nutrients, inert matter, stability etc. in the mature compost. Typical quality parameters are presented in Table 6. The properties of the compost standard leachate may also be considered. Heavy metals and persistent organic pollutants accumulate in the compost and may cause problems during utilization. Compost quality depends on quality of the input material, which should be carefully controlled by input analysis. Pathogenic bacteria may originate from the mesophilic digestates or from infected co- composting materials, if applied (e.g. food waste). If thermophilic phase period of the composting process has lasted at least few days, the compost produced may be considered sanitized and free of pathogens such as Salmonella, Streptococci and coliforms. Management of Organic Waste 24 The third important factor is presence of nitrogen. Several authors have reported that the optimal C/N ratio is between 25/1 and 30/1 although operation at low C/N ratios of 10/1 are also possible. With such low C/N ratios the undesirable emission of ammonia can be significant (Matsumura et al., 2010). Characteristic values of organic matter content and total nitrogen in the digested sludge are 50-70% and 1.5-2.5%, respectively. In the first week of the digested sludge composting the total carbon is reduced by between 11% and 27% and total nitrogen is reduced by between 13% and 23% (Pakou et al., 2009; Yañez et al., 2009). Parameter Test method Limit value 1. Pathogens Escherichia coli Salmonella sp. ISO 16649-2 1000 CFU/g fresh matter Absent in 25 g fresh matter 2. Toxic elements Cd Cr Cu Hg Ni Pb Zn EN 13650 EN 13650 EN 13650 ISO 16772 EN 13650 EN 13650 EN 13650 1.5 mg/kg d.m. 100 mg/kg d.m. 200 mg/kg d.m. 1.0 mg/kg d.m. 50 mg/kg d.m. 200 mg/kg d.m. 400 mg/kg d.m. 3. Stability Volatile faty acids Residual biogas potential GC - 0.25 l/gVS 4. Physical contaminants Total glass, metal, plastic and other man- made fragments Stones >5 mm 0.5 % m/m d.m. 8 % m/m d.m. 5.Parameters for declaration Total nitrogen Total phosphorus Total potassium Water soluble chloride Water soluble sodium Dry matter Loss on ignition pH EN 13654 EN 13650 EN 13650 EN 13652 EN 13652 EN 14346 EN 15169 EN 13037 - Table 6. Control parameters of digestate quality for application in agriculture (WRAP 2010) Highest degradation rates in the compost pile are achieved with air oxygen concentration above 15% which also prevents formation of anaerobic zones. The quality of aeration depends primarily on structure and degree of granulation of the composting material; finer materials generally provide better aeration of the compost pile (Sundberg and Jönsson, 2008). In the first stages of degradation, acids are generated, and these tend to decrease the pH in the compost pile. The optimum pH range for microorganisms to function is between 5.5 and 8.5. Elevated temperature in the compost material during operation is a consequence of exothermic organic matter degradation process. The optimum temperature for Anaerobic Treatment and Biogas Production from Organic Waste 25 composting operation, in which pathogenic microorganisms are sanitised, is 55-70°C. In the initial phases of composting the prevailing microorganisms are fungi and mesophilic bacteria, which contribute to the temperature increase and are mostly sanitised in the relevant thermophilic range. When temperature falls many of the initial mesophilic microorganisms reappear, but the predominant population are more highly evolved organisms such as protozoa and arthropods (Schuchard, 2005). For optimum composting operation the correct conditions must be established and are determined by particle size distribution and compost pile aeration have shown that the air gaps in the compost pile can be reduced from an initial 76.3% to a final 40.0%. The optimum moisture content in the compost material is in the range of 50-70%. In the recent years the composting practice for anaerobic digestate has been thoroughly studied for many different types of substrates, for co-composting and with many different bulk agents (Nakasaki et al., 2009; Himanen et al., 2011). From various reasons the composting of the digestate residue is sometimes not possible (lack of space, problems with compost disposal etc.). Alternatively the digestate may be treated by thermal methods, which require higher solid content. Mechanical dehydration by means of continuous centrifuges provides solid content about 30 % with positive calorific value. Incineration may be carried out in a special kiln (most often of fluidized bed type) or together with municipal waste in a grit furnace. Co-incineration in industrial kilns usually require drying of sludge to 90 % dryness, that gives calorific value of about 10 MJ/kg. Thermal methods are more expensive than composting due to high energy demand for dehydration and drying, sophisticated processes invplved and strict monitoring requirements. Good review of the modern alternative processes of anaerobic sludge treatment is presented by Rulkens (2008). 4. Conclusions The chapter entitled “Sustainable Treatment of Organic Wastes” presents principles and techniques for treatment of wet biodegradable organic waste, which can be applied in order to achieve environmental as well as economic sustainability of their utilisation. The chapter mostly focuses on organic wastes generated in the municipal sector; however it may well apply to similar wastes from agriculture and industry. The main focus is aimed at matching the anaerobic treatment process to the selected type of waste in order to maximize the biogas production, a valuable renewable energy resource. The chapter also focuses on technological aspects of the technology used in such treatments and presents and elaborates several conventional treatments (such as semi-continuous processes, two stage processes, sequencing batch processes, etc.) as well as some emerging technologies which have only recently gained some ground (such as anaerobic treatment in solid state). The basic conditions are presented which are required to successfully design and operate the treatment process. Organic loading rates, biogas production rates, specific biogas productivity, biogas potentials and specific concerns for certain technologies and waste substrates are presented. The main influencing factors such as environmental conditions (pH, temperature, alkalinity, etc.) have been addressed as well as inhibitors that can arise in such processes (heavy metals, ammonia, salts, phenolic compounds from lignocellulosic degradation, organic overload etc.). The biogas treatment and use, such as power Management of Organic Waste 26 production and natural gas grid injection, have been presented as well as the use of parasitic energy, options for biogas production enhancement through waste pre-treatment (mechanical, chemical, physical, etc.) and treatment of residues of anaerobic digestion, which may have an important impact on the environment. Special attention is given to further treatment of digested solid residues as well. Due attention is paid to aerobic stabilization processes (open and closed composting), taking into account physical form of the waste, its composition, pollution, degradability and final deposition and use. 5. Acknowledgment The authors express acknowledgements to Slovenian biogas producers and to the Slovenian Science and Research Agency, whose support in anaerobic digestion and waste treatment research has lead to the knowledge presented here. 6. References Banegas V., J.L. Moreno, J.I. Moreno, C. Garcia, G. Leon, T. Hernandez, (2007). Composting anaerobic and aerobic sewage sludges using two proportions of sawdust. Waste Manag. 27, 1317-27 Behrendt F.; Sieverding M., (2010). “Biogas-Einspeisung in Erdgasnetze aus Netzbetreibersicht”, GWF Das Gas- und Wasserfach, Gas – Erdgas, 151(3), p. 140- 144. De Gioannis G., Diaz L.F., Muntoni A., Pisanu A., (2008). "Two-phase anaerobic digestion within a solid waste/wastewater integrated management system." Waste Management 28(10): 1801-1808. Deublein, D. and A. Steinhauser (2008). Biogas from waste and renewable resources. Weinheim, Willey-VCH Verlag GmbH & Co. KGaA. Dinsdale R. M., Premier G.C., Hawkes F.R., Hawkes D.L., (2000). "Two-stage anaerobic co- digestion of waste activated sludge and fruit/vegetable waste using inclined tubular digesters." Bioresource Technology 72(2): 159-168. DVGW - Deutscher Verein des Gas- und Wasserfaches, DVGW G 262 “Nutzung von Gasen aus regenerativen Quellen in der der Öffentlichen Gasversorgung”(2010), available online with limited access at http://www.dvgw.de/gas/gesetze-und-erordnungen/. Feijoo G., Soto M., Méndez R., Lema J.M., (1995). "Sodium inhibition in the anaerobic digestion process: antagonism and adaptation phenomena." Enzym Microb Technol 17(2): 180-188. GNS (2009) Nitrogen removal from manure and organic residues by ANAStrip - process (System GNS). http://www.gns-halle.de/english/site_1_6.htm (Access 11 th August 2011). Han Y., Sung S., Dague R.R., (1997). "Temperature-phased anaerobic digestion of wastewater sludges." Water Sci Technol 36(6-7): 367-374. Hendriks A.T.W.M., Zeeman G., (2009). "Pretreatments to enhance the digestibility of lignocellulosic biomass." Bioresour Technol 100(1): 10-18. Himanen M., Hänninen K., (2011). Composting of bio-waste, aerobic and anaerobic sludges– Effect of feedstock on the process and quality of compost. Bioresource Technology, Volume 102, Issue 3, p. 2842-2852. Anaerobic Treatment and Biogas Production from Organic Waste 27 ISO (1998) EN ISO 11734 (1998) Water Quality – Evaluation of the »Ultimate« Anaerobic Biodegradability of Organic Compounds in Digested Sludge – Method by Measurement of the Biogas Production, International Standard Organization. Kompogas, (2011). " Green energy from organic waste." Retrieved 11 th August 2011, from http://www.axpo-kompogas.ch/index.php?path=home&lang=en. Messenger J., de Villers H.A., Laubscher S.J.A., Kenmuir K. and Ekama G.A. (1993). "Evaluation of the Dual Digestion System: Part 1: Overview of the Milnerton Experience." Water SA 19(3): 185-192. Mrafkova L., Goi D., Gallo V., Colussi I., (2003). "Preliminary Evaluation of Inhibitory Effects of Some Substances on Aerobic and Anaerobic Treatment Plant Biomasses." Chem Biochem Eng Q 17(3): 243-247. Nakasaki K., Tran L.T.H., Idemoto Y., Abe M., Rollon A.P., (2009). Comparison of organic matter degradation and microbial community during thermophilic composting of two different types of anaerobic sludge. Bioresource Technology, Volume 100, Issue 2, p. 676-682. Polprasert C. (2007) Organic Waste Recycling – Technology and Management, 3 rd Ed., e- book, IWA Publishing , London http://books.google.si/books?id=owycqJMjoZoC&printsec=frontcover&dq=Orga nic+waste+recycling:+technology+and+management&source=bl&ots=kZC9lGSJFb &sig=T_rGd1UQVQL3dLDmbacV87jNXEQ&hl=sl&ei=- Ponsá S., Ferrer I., Vázquez F., Font X. (2008). "Optimization of the hydrolytic-acidogenic anaerobic digestion stage (55 °C) of sewage sludge: Influence of pH and solid content." Water Res 42(14): 3972-3980. Pöschl M., Ward S., Owende P., (2010). “Evaluation of energy efficiency of various biogas production and utilization pathways”Applied Energy, 87 (11), p. 3305-3321. Roberts R., Davies W.J., Forster C.F., (1999). "Two-Stage, Thermophilic-Mesophilic Anaerobic Digestion of Sewage Sludge." Process Saf Environ Protec 77(2): 93-97. Rulkens W., (2008). Sewage Sludge as a Biomass Resource for the Production of Energy: Overview and Assessment of the Various Options, Energy Fuels, 22 (1), pp 9–15 Ryckebosch E., Drouillon M., Vervaeren H., (2011). “Techniques for transformation of biogas to biomethane”, Biomass and Bioenergy, 35(5), p. 1633-1645. Sattler. (2009). "Biogas storage systems." Retrieved 11.8.2011, from http://www.sattler- ag.com/sattler-web/en/products/190.htm Schuchard F., (2005). Composting of organic waste. In: Enviromental biotechnology concepts and aplications. Editors:Jördering, H.J., Winter, J. Weinheim: Willey-VCH Verlag, p. 333-354. Sežun M., Grilc V., Zupančič G.D. and Marinšek-Logar R., (2011). Anaerobic digestion of brewery spent grain in a semi-continuous bioreactor: inhibition by phenolic degradation products. Acta chim. slov , 58, 1, 158-166. Song Y.C., Kwon S.J., Woo J.H., (2004). "Mesophilic and thermophilic temperature co-phase anaerobic digestion compared with single-stage mesophilic- and thermophilic digestion of sewage sludge." Water Research 38(7): 1653-1662. Sundberg C., Jönsson H., (2008). Higher pH and faster decomposition in biowaste compostingby increased aeration. Waste Management, Volume 28, Issue 3, p. 518- 526. Management of Organic Waste 28 Sung, S. and T. Liu (2003). "Ammonia inhibition on thermophilic anaerobic digestion." Chemosphere 53: 43-52. Tubtong C., Towprayoon S., Connor M.A., Chaiprasert P., Nopharatana A., (2010). “Effect of recirculation rate on methane production and SEBAR system performance using active stage digester.” Waste Management & Research, 28(9): 818-827. Tapana C., Krishna P.R., (2004). "Anaerobic Thermophilic/Mesophilic Dual-Stage Sludge Treatment." Journal of Environmental Engineering 126(9): 796-801. Tarrasón, D., Ojeda, G., Ortiz, O., Alcañiz, J.M., (2008). Differences on nitrogen availability in a soil amended with fresh, composted and thermally-dried sewage sludge. Bioresource Technology, Volume 99, Issue 2, p. 252-259. Verordnung zut Anderung der Gesetzzugangsverordnung, das Gasnetzentgeltverodnung, der Anreizregulierungsverordnung und der Stromnetzentgeltverordnung, Bundesgesetzblatt Jahrgang 2008 Teil I Nr. 14 11. April 2008 (S. 693÷697) WRAP (2010) Specification for whole digestate, separated digestate, separated liquor and separated fibre derived from the anaerobic digestion of source-segregated biodegradable materials, Publicly Available Specification (PAS) 110, U.K. Yañez R., Alonso J.L., Díaz M.J., (2009). Influence of bulking agent on sewage sludge composting process, Bioresource Technology, Volume 100, Issue 23, p. 5827-5833. Ye C., Cheng J.J., Creamer K.S., (2008). "Inhibition of anaerobic digestion process: A review." Bioresource Technology 99(10): 4044-4064. Zupančič G. D., Roš M., (2003). "Heat and energy requirements in thermophilic anaerobic sludge digestion." Renewable Energy 28(14): 2255-2267. Zbytniewski, R., Buszewski, B., 2005. Characterization of natural organic matter (NOM) derived from sewage sludge compost. Part 1: chemical and spectroscopic properties. Bioresource Technology, Volume 96, Issue 4, p. 471-478. 2 Vermicomposting: Composting with Earthworms to Recycle Organic Wastes Jorge Domínguez 1 and María Gómez-Brandón 2 1 Universidade de Vigo 2 University of Innsbruck 1 Spain 2 Austria 1. Introduction The overproduction of organic wastes has led to the use of inappropriate disposal practices such as their indiscriminate and inappropriately-timed application to agricultural fields. These practices can cause several environmental problems, including an excessive input of potentially harmful trace metals, inorganic salts and pathogens; increased nutrient loss, mainly nitrogen and phosphorus, from soils through leaching, erosion and runoff; and the emission of hydrogen sulphide, ammonia and other toxic gases (Hutchison et al., 2005). However, if handled properly, organic wastes can be used as valuable resources for renewable energy production, as well as sources of nutrients for agriculture, as they provide high contents of macro- and micronutrients for crop growth and represent a low-cost alternative to mineral fertilizers (Moral et al., 2009). The health and environmental risks associated with the management of such wastes could be significantly reduced by stabilizing them before their disposal or use. Composting and vermicomposting are two of the best known-processes for the biological stabilization of a great variety of organic wastes (Domínguez & Edwards, 2010a). However, more than a century had to pass until vermicomposting, i.e. the processing of organic wastes by earthworms was truly considered as a field of scientific knowledge or even a real technology, despite Darwin (1881) having already highlighted the important role of earthworms in the decomposition of dead plants and the release of nutrients from them. In recent years, vermicomposting has progressed considerably, primarily due to its low cost and the large amounts of organic wastes that can be processed. Indeed, it has been shown that sewage sludge, paper industry waste, urban residues, food and animal waste, as well as horticultural residues from cultivars may be successfully managed by vermicomposting to produce vermicomposts for different practical applications (reviewed in Domínguez, 2004). Vermicompost, the end product of vermicomposting, is a finely divided peat-like material of high porosity and water holding capacity that contains many nutrients in forms that are readily taken up by plants. Vermicomposting is defined as a bio-oxidative process in which detritivore earthworms interact intensively with microorganisms and other fauna within the decomposer community, accelerating the stabilization of organic matter and greatly modifying its Management of Organic Waste 30 physical and biochemical properties (Domínguez, 2004). The biochemical decomposition of organic matter is primarily accomplished by microorganisms, but earthworms are crucial drivers of the process as they may affect microbial decomposer activity by grazing directly on microorganisms (Aira et al., 2009; Monroy et al., 2009; Gómez-Brandón et al., 2011a), and by increasing the surface area available for microbial attack after comminution of organic matter (Domínguez et al., 2010) (Figure 1). These activities may enhance the turnover rate and productivity of microbial communities, thereby increasing the rate of decomposition. Earthworms may also affect other fauna directly, mainly through the ingestion of microfaunal groups (protozoa and nematodes) that are present within the organic detritus consumed (Monroy et al., 2008); or indirectly, modifying the availability of resources for these groups (Monroy et al., 2011) (Figure 1). Fig. 1. Positive (+) and negative (-) effects of earthworms on microbiota and microfauna (modified from Domínguez et al., 2010). Furthermore, earthworms are known to excrete large amounts of casts (Figure 1), which are difficult to separate from the ingested substrate (Domínguez et al., 2010). The contact between worm-worked and unworked material may thus affect the decomposition rates (Aira & Domínguez, 2011), due to the presence of microbial populations in earthworm casts different from those contained in the material prior to ingestion (Gómez-Brandón et al., 2011a). In addition, the nutrient content of the egested materials differs from that in the ingested material (Aira et al., 2008), which may enable better exploitation of resources, because of the presence of a pool of readily assimilable compounds in the earthworm casts. Therefore, the decaying organic matter in vermicomposting systems is a spatially and temporally heterogeneous matrix of organic resources with contrasting qualities that result from the different rates of degradation that occur during decomposition (Moore et al., 2004). [...]... and inoculated with 25 mature individuals of the earthworm species E andrei The microcosms consisted of 250 mL plastic 34 Management of Organic Waste containers filled to three quarters of their capacity with sieved, moistened vermiculite A plastic mesh was placed over the surface of the vermiculite and 100 g (fresh weight, fw) of the substrate was placed on top of the mesh, to avoid mixing the substrate... rate at which the residue is applied (Aira & Domínguez, 2008) More specifically, the impact of earthworms on the decomposition of organic waste during the vermicomposting process is initially due to gut associated processes (GAPs) (Figure 3) , i.e., via the effects of ingestion, digestion and assimilation of the organic matter and microorganisms in the gut, and then casting (Gómez-Brandón et al., 2011a)... presence and abundance of microorganisms during the passage of organic material through the gut of these earthworm species have been observed For instance, some bacteria are activated during passage through the gut, whereas others remain GAPs: Gut associated processes CAPs: Cast associated processes Casts GAPs CAPs Organic matter Fig 3 Earthworms affect the decomposition of organic matter during vermicomposting... excavatus (bottom right) 32 Management of Organic Waste 3 How does vermicomposting work? The vermicomposting process includes two different phases regarding earthworm activity: (i) an active phase during which earthworms process the organic substrate, thereby modifying its physical state and microbial composition (Lores et al., 2006), and (ii) a maturation phase marked by the displacement of the earthworms... individuals) n=5 b) Microcosm incubation Sample collection 20 °C 3 days 24 h Fig 4 Scheme of the (a) microcosm and (b) procedure for incubation of microcosms and collection of cast samples Vermicomposting: Composting with Earthworms to Recycle Organic Wastes 35 microbial activity was determined by hydrolysis of fluorescein diacetate (FDA), a colourless compound that is hydrolysed by both free and... Vermicomposting: Composting with Earthworms to Recycle Organic Wastes 33 unaffected and others are digested in the intestinal tract and thus decrease in number (Drake & Horn, 2007; Monroy et al., 2009) Such selective effects on microbial communities as a result of gut transit may alter the decomposition pathways during vermicomposting, probably by modifying the composition of the microbial communities involved in... functional diversity of microbial populations in vermicomposting systems (Aira & Domínguez, 2011) Upon completion of GAPs, the resultant earthworm casts undergo cast associated processes (CAPs; Figure 3) , which are more closely related to ageing processes, the presence of unworked material and to physical modification of the egested material (weeks to months) During these processes the effects of earthworms... species affect the structure and activity of microbial communities during the active phase of vermicomposting iii To investigate the effectiveness of the active phase of vermicomposting for the shortterm stabilization of a plant residue 4.1 How do earthworms affect microbial communities through the gut associated processes? To provide further light into the effect of gut transit on microbial communities,... mounds and herbivore dungs, as well as in man-made environments such as manure heaps These latter species, with their natural ability to colonize organic wastes; high rates of consumption, digestion and assimilation of organic matter; tolerance to a wide range of environmental factors; short life cycles, high reproductive rates, and endurance and resistance to handling show good potential for vermicomposting...Vermicomposting: Composting with Earthworms to Recycle Organic Wastes 31 2 Earthworm species suitable for vermicomposting Earthworms represent the major animal biomass in most terrestrial temperate ecosystems (Edwards & Bohlen, 1996) Indeed, more than 8 ,30 0 species of earthworms have been described (Reynolds & Wetzel, 2010), although for the great majority of these species only the names and morphologies . Dry matter Loss on ignition pH EN 136 54 EN 136 50 EN 136 50 EN 136 52 EN 136 52 EN 1 434 6 EN 15169 EN 130 37 - Table 6. Control parameters of digestate quality for application in. stabilization of organic matter and greatly modifying its Management of Organic Waste 30 physical and biochemical properties (Domínguez, 2004). The biochemical decomposition of organic matter. Volume 28, Issue 3, p. 518- 526. Management of Organic Waste 28 Sung, S. and T. Liu (20 03) . "Ammonia inhibition on thermophilic anaerobic digestion." Chemosphere 53: 43- 52. Tubtong